Hi Frieda, and welcome to DC.
You can freeze buttercream frosting quite well. What I do with my wedding cakes (specially the top layers the brides want to keep) is to put it in the freezer as is (carefully so nothing is touching it) for about an hour and then take it out and wrap it tightly but gently with plastic wrap. The first freezing makes the icing hard and the wrap won't damage it. Then I just put it in a plastic container and put it in the freezer. You can keep it for quite awhile, depending on the cake, not the frosting. Don't leave it uncovered for more than an hour, and check it after a half hour to see if it is firm - you don't want frost to form.
Hope that helps.
"Variety is not just the spice of life, it is the key to life" - Chef Michael Smith